Latex for dip molding, composition for dip molding, preparation method of dip molded product, and dip molded product prepared thereby

ABSTRACT

Provided are a latex for dip molding, a composition for dip molding, a preparation method of a dip molded product, and a dip molded product prepared thereby. The latex for dip molding includes a conjugated diene monomer, an ethylenically unsaturated nitrile monomer, and an ethylenically unsaturated acid monomer, wherein the latex further includes sodium methallyl sulfonate as a copolymerizable ionic monomer. A dip molded product having excellent tensile strength, elongation, and touch may be obtained from a composition using the latex according to the present invention, and the generation of limitations, such as non-uniformity of physical properties and difficulties in product management, may be prevented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of PCT InternationalApplication No. PCT/KR2010/003766, filed Jun. 11, 2010, which claims thebenefit of Patent Application No. 10-2009-0052288 filed in Korea on Jun.12, 2009. The entire contents of all of the above applications arehereby incorporated by reference into the present application.

BACKGROUND

The present invention disclosed herein relates to a dip molded producthaving excellent tensile strength, elongation, and touch, a preparationmethod thereof, a composition for dip molding for preparing the dipmolded product, and a latex for dip molding used in the composition fordip molding.

A natural rubber latex has typically been used as a raw material for dipmolded products such as rubber gloves, but recently, there arelimitations in that a protein in the natural rubber latex causes rash,itchiness, or common cold by allergic reactions occurred when theprotein is in contact with human skin. Accordingly, a carboxylatedacrylonitrile-butadiene-based copolymer latex, a synthetic rubber latexwithout including a protein, receives attention and the use amountthereof tends to increase.

In addition, high levels of physical properties, such as tensilestrength, elongation, and touch, are recently required for a dip moldedproduct obtained by using a typical composition for dip molding, whilehigh qualities are needed with respect to a latex for dip moldingaccording to the increase in the use amount thereof.

When the stability of a composition for dip molding is maintained,tensile strength, elongation, and touch of a dip molded product may beimproved. When the stability of the composition for dip molding is notmaintained, it may cause significant loss to a manufacturer of dipmolded products because tensile strength, elongation, and touch of thedip molded products significantly decrease as well as the occurrence oflimitations, such as flow marks and pinholes of the dip molded products.The foregoing stability of the composition for dip molding becomes moreimportant in order to obtain high qualities of the dip molded productand may be an important factor in determining productivity of the dipmolded product.

In many cases, the stability of the composition for dip molding commonlydepends on a latex for dip molding. A latex used in the composition fordip molding is generally a carboxylated acrylonitrile-butadiene-basedlatex and the stability thereof is maintained by a carboxylic group andan emulsifier on a surface thereof. Typically, the carboxylic group maybe obtained by using an ethylenically unsaturated acid as acopolymerizable monomer and the carboxylic group may increase stabilityby being fixed on a latex surface. However, in many cases, thecarboxylic group may not provide sufficient chemical stability in a pHrange of 9 to 12, a pH range of a typical composition for dip molding.

Therefore, an emulsifier is used for the chemical stability of thecomposition. Although the emulsifiers may differ according to afunctional group thereof, the stability may be increased by using agenerally used anionic emulsifier having a functional group, such assulfate and sulfonate, or an ethylene oxide-based non-ionic emulsifier.However, since the emulsifier, different from the carboxylic group, isnot fixed but absorbed on a latex, there are limitations in thatefficiency for the stability may decrease by desorption occurred duringthe application of mechanical shear and the generation of gas bubblesmay be severe.

Also, a scale problem may be generated as one of great difficulties inpreparation of the latex for dip molding. A large amount of scales maybe generated in a reactor or on an agitator during the preparation ofthe latex according to characteristics thereof. Since the scales maycause a lot of problems such as non-uniformity of physical propertiesduring a continuous process by acting as an impurity during a subsequentprocess and great time and efforts may be required to remove the scales,the scales may greatly influence on the reduction of productivity.

Different from the scales formed in the reactor, coagulums may exist ina suspension and are filtered through screening after the completion ofpolymerization and during the preparation of the composition for dipmolding. Product management may be difficult because a lot of time andcosts are used for the filtration thereof and qualities of a dip moldedproduct may deteriorate because fine agglomerates may appear in the dipmolded product during dip molding.

SUMMARY

The present invention provides a dip molded product having excellenttensile strength, elongation, and touch.

The present invention also provides relative improvements of qualitiesthrough preventing the generation of limitations such as non-uniformityof physical properties and difficulties in product management bydecreasing an amount of impurities such as scales generated during apreparation process of the dip molded product.

Embodiments of the present invention provide a latex for dip moldingincluding: a conjugated diene monomer, an ethylenically unsaturatednitrile monomer, and an ethylenically unsaturated acid monomer, whereinthe latex may further include a sodium methallyl sulfonate as acopolymerizable ionic monomer.

In some embodiments, contents of the foregoing components may be about0.1 to 10 parts by weight of the sodium methallyl sulfonate based on 100parts by weight of a monomer mixture including about 40 to 90 wt % ofthe conjugated diene monomer, about 9 to 50 wt % of the ethylenicallyunsaturated nitrile monomer, and about 0.1 to 10 wt % of theethylenically unsaturated acid monomer.

In other embodiments, the conjugated diene monomer may be 1,3-butadiene,2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene,isoprene, or a mixture thereof.

In still other embodiments, the ethylenically unsaturated nitrilemonomer may be acrylonitrile, methacrylonitrile, fumalonitrile,α-chloronitrile, α-cyanoethyl acrylonitrile, or a mixture thereof.

In even other embodiments, the ethylenically unsaturated acid monomermay be an ethylenically unsaturated carboxylic acid monomer, apolycarboxylic acid anhydride, an ethylenically unsaturated sulfonicacid monomer, an ethylenically unsaturated polycarboxylic acid partialester monomer, or a mixture thereof.

In yet other embodiments, the latex may further include about 0.1 to 20wt % of other ethylenically unsaturated monomers copolymerizable withthe ethylenically unsaturated nitrile monomer and the ethylenicallyunsaturated acid monomer among total monomers.

In further embodiments, the other ethylenically unsaturated monomerscopolymerizable with the ethylenically unsaturated nitrile monomer andthe ethylenically unsaturated acid monomer may be a vinyl aromaticmonomer, a fluoroalkylvinyl ether, an ethylenically unsaturated amidmonomer, vinyl pyridine, vinyl norbornene, a non-conjugated dienemonomer, an ethylenically unsaturated carboxylic acid ester monomer, andmixtures thereof.

In still further embodiments, emulsion polymerization may be performedby further including an emulsifier, a polymerization initiator, a chaintransfer agent, a polymerization terminating agent, or a mixture thereofduring the emulsion polymerization of the monomers.

In even further embodiments, the emulsifier may be an alkyl benzenesulfonate, an alcohol sulfate, an alcohol ether sulfonate, an alkylphenol ether sulfonate, an alpha olefin sulfonate, a paraffin sulfonate,an ester sulfosuccinate, a phosphate ester, an alkyl phenol ethoxylate,a fatty amine ethoxylate, a fatty acid ethoxylate, an alkanoamide, or amixture thereof.

In yet further embodiments, the coagulant may be barium chloride,calcium chloride, magnesium chloride, zinc chloride, aluminum chloride,barium nitrate, calcium nitrate, zinc nitrate, barium acetate, calciumacetate, zinc acetate, calcium sulfate, magnesium sulfate, and aluminumsulfate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates to a latex for dip molding including aconjugated diene monomer, an ethylenically unsaturated nitrile monomer,and an ethylenically unsaturated acid monomer, and more particularly, toa latex for dip molding further including a sodium methallyl sulfonateas a copolymerizable ionic monomer.

Also, the present invention provides a composition for dip moldingcontaining the latex for dip molding.

Also, the present invention provides a method of preparing a dip moldedproduct including: (a) dipping a dip mold in a coagulant solution toattach the coagulant onto a surface of the dip mold; (b) dipping the dipmold having the attached coagulant in the composition to form a dipmolded layer; (c) heat treating the dip molded layer formed on the dipmold to cross-link a latex resin.

Further, the present invention provides a dip molded product preparedaccording to the foregoing method.

Hereinafter, the present invention will be described in more detail.

A latex composition for dip molding of the present invention includes0.1 to 10 parts by weight of a sodium methallyl sulfonate based on 100parts by weight of a monomer mixture including 40 to 90 wt % of aconjugated diene monomer, 9 to 50 wt % of an ethylenically unsaturatednitrile monomer, and 0.1 to 10 wt % of an ethylenically unsaturated acidmonomer.

The present invention discovered that mechanical and chemicalstabilities of a latex may be significantly increased by using an ionicmonomer copolymerizable on a latex surface. That is, since the ionicmonomer having high solubility is fixed onto the latex surface bycopolymerization, stability may be significantly increased by preventingthe reduction of stability due to desorption and the generation of gasbubbles.

The present invention provides a latex for dip molding, in whichstability thereof is significantly improved by using a sodium methallylsulfonate, an ionic monomer particularly exhibiting innovative physicalproperties among the foregoing ionic monomers, and a composition for dipmolding using the sodium methallyl sulfonate.

Since the sodium methallyl sulfonate copolymerizable ionic monomersuggested in the present invention may act to provide the stability ofthe latex which may not be sufficiently obtained with an emulsifier, thesodium methallyl sulfonate may be used by adjusting and mixing theamount thereof with respect to emulsifiers to be described later. Theuse amount of the sodium methallyl sulfonate may be in a range of 0.1 to10 parts by weight based on 100 parts by weight of the monomer, and, forexample, may be in a range of 0.1 to 5 parts by weight. When the useamount of the sodium methallyl sulfonate is less than 0.1 parts byweight, the effect thereof may not be obtained, and when the use amountthereof is greater than 10 parts by weight, polymerization stability andthe qualities of the dip molded product may instead deteriorate due toan excessive amount of ionic polymers included.

The conjugated diene monomer used in the present invention may be usedalone or in combination of two or more selected from the groupconsisting of 1,3-butadiene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 1,3-pentadiene, isoprene, or a mixture thereof.1,3-butadiene and isoprene may be used among the foregoing conjugateddiene monomers and, for example, 1,3-butadiene may particularly be used.

The used amount of the conjugated diene monomer is in a range of 40 wt %to 90 wt % among total monomers, and, for example, may be in a range of45 wt % to 80 wt %. When the amount of the conjugated diene monomer istoo small, the latex resin molded product becomes hard and touch becomespoor. On the other hand, when the amount of the conjugated diene monomeris too large, tensile strength of the latex resin molded productdecreases.

The ethylenically unsaturated nitrile monomer used in the presentinvention may be used alone or in combination of two or more selectedfrom the group consisting of acrylonitrile, methacrylonitrile,fumalonitrile, α-chloronitrile, α-cyanoethyl acrylonitrile, or a mixturethereof. Among the foregoing ethylenically unsaturated nitrile monomers,acrylonitrile and methacrylonitrile may be used and, for example,acrylonitrile may particularly be used.

The used amount of the ethylenically unsaturated nitrile monomer is in arange of 9 wt % to 50 wt % among the total monomers, and, for example,may be in a range of 15 wt % to 45 wt %. When the amount of theethylenically unsaturated nitrile monomer is too small, tensile strengthof the latex resin molded product decreases, and when the amount of theethylenically unsaturated nitrile monomer is too large, the latex resinmolded product becomes hard and touch becomes poor.

The ethylenically unsaturated acid monomer used in the present inventionis an ethylenically unsaturated monomer containing an acid group, suchas a carboxyl group, a sulfonic acid group, and an acid anhydride group.Examples of the ethylenically unsaturated acid monomer may beethylenically unsaturated carboxylic acid monomers such as an acrylicacid, a methacrylic acid, an itaconic acid, a maleic acid, and a fumaricacid; polycarboxylic acid anhydrides such as a maleic anhydride and acitraconic anhydride; ethylenically unsaturated sulfonic acid monomerssuch as a styrenesulfonic acid; ethylenically unsaturated polycarboxylicacid partial ester monomers such as a monobutyl fumarate, a monobutylmaleate, and a mono-2-hydroxypropyl maleate. The ethylenicallyunsaturated carboxylic acid monomer may be used among the foregoingethylenically unsaturated acid monomers, and the methacrylic acid mayparticularly be used. The ethylenically unsaturated acid monomer may beused in the form of an alkali metal salt or an ammonium salt. Theethylenically unsaturated acid monomer may be used alone or incombination of two or more thereof.

The used amount of the ethylenically unsaturated acid monomer is in arange of 0.1 wt % to 10 wt % among the total monomers, may be in a rangeof 0.5 wt % to 9 wt %, and, for example, may be in a range of 1 wt % to8 wt %. When the amount of the ethylenically unsaturated acid monomer istoo small, tensile strength of the latex resin molded product decreases,and when the amount of the ethylenically unsaturated acid monomer is toolarge, the latex resin molded product becomes hard and touch becomespoor.

The latex of the present invention may further include otherethylenically unsaturated monomers copolymerizable with theethylenically unsaturated nitrile monomer and the ethylenicallyunsaturated acid monomer. Particular examples thereof may be vinylaromatic monomers such as styrene, alkyl styrene, and vinyl naphthalene;fluoroalkylvinyl ethers such as a fluoro ethyl vinyl ether;ethylenically unsaturated amid monomers such as (meth)acrylamid,N-methylol (meth)acrylamid, N,N-dimethylol (meth)acrylamid, N-methoxymethyl(meth)acrylamid, and N-propoxy methyl(meth)acrylamid; vinylpyridine; vinyl norbornene; non-conjugated diene monomers such asdicyclo pentadiene and 1,4-hexadiene; ethylenically unsaturatedcarboxylic acid ester monomers such as methyl (meth)acrylate, ethyl(meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, dibutylmaleate, dibutyl fumarate, diethyl maleate, methoxymethyl(meth)acrylate, ethoxyethyl (meth)acrylate, methoxyethoxyethyl(meth)acrylate, cyanomethyl (meth)acrylate, 2-cyanoethyl (meth)acrylate,1-cyanopropyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate,3-cyanopropyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, glycidyl (meth)acrylate, and dimethylaminoethyl(meth)acrylate. The ethylenically unsaturated monomer may be used aloneor in combination of two or more thereof. The use amount of theethylenically unsaturated monomer is in a range of 0.1 wt % to 20 wt %among the total monomers. When the use amount of the ethylenicallyunsaturated monomer is too large, soft touch and tensile strength arenot balanced well.

In the present invention, emulsion polymerization may be performed byfurther including an emulsifier, a polymerization initiator, a chaintransfer agent, a polymerization terminating agent, or a mixture thereofduring the emulsion polymerization of the monomers.

The emulsifier used in the present invention is introduced in order toprovide stability to the latex during and after a polymerizationreaction, and various types of anionic emulsifiers and non-ionicemulsifiers may be used. Examples of the anionic emulsifier may be alkylbenzene sulfonates such as a sodium alkyl benzene sulfonate, an alcoholsulfate, an alcohol ether sulfonate, an alkyl phenol ether sulfonate, analpha olefin sulfonate, a paraffin sulfonate, an ester sulfosuccinate,and a phosphate ester. Examples of the non-ionic emulsifier may be analkyl phenol ethoxylate, a fatty amine ethoxylate, a fatty acidethoxylate, and an alkanoamide. The emulsifier may be used alone or incombination of two or more thereof. The use amount thereof is in a rangeof 0.5 to 10 parts by weight based on 100 parts by weight of themonomer.

The polymerization initiator is not particularly limited, but a radicalinitiator may be used as the polymerization initiator. Examples of theradical initiator may be inorganic peroxides such as a sodiumpersulfate, a potassium persulfate, an ammonium persulfate, a potassiumperphosphate, and a hydrogen peroxide; organic peroxides such as at-butyl peroxide, a cumene hydroperoxide, a p-menthane hydroperoxide, adi-t-butyl peroxide, a t-butylcumyl peroxide, an acetyl peroxide, anisobutyl peroxide, an octanoyl peroxide, a dibenzoyl peroxide, a3,5,5-trimethylhexanol peroxide, and a t-butylperoxy isobutyrate;nitrogen compounds such as azobisisobutyronitrile,azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, andmethyl azobisisobutyrate. The polymerization initiator may be used aloneor in combination of two or more thereof. The inorganic peroxide or theorganic peroxide may be used among the foregoing radical initiators, theinorganic peroxide, for example, may be used, and the persulfate mayparticularly be used. The use amount of the polymerization initiator maybe in a range of 0.01 to 2 parts by weight based on 100 parts by weightof the monomer and, for example, may be in a range of 0.02 to 1.5 partsby weight.

The chain transfer agent is not particularly limited, and examples ofthe chain transfer agent may be mercaptans such as α-methylstyrenedimer,t-dodecyl mercaptan, n-dodecyl mercaptan, octyl mercaptan; halogenatedhydrocarbons such as carbon tetrachloride, methylene chloride, andmethylene bromide; sulfur-containing compounds such as tetraethylthiuramdisulfide, dipentamethylenethiuram, disulfide, and diisopropylxanthogendisulfide. The chain transfer agent may be used alone or in combinationof two or more thereof. The mercaptans may be used among the foregoingchain transfer agents and, for example, the t-dodecyl mercaptan may beused. The use amount of the chain transfer agent may be in a range of0.1 to 0.9 parts by weight based on 100 parts by weight of the monomerand, for example, may be in a range of 0.2 to 0.7 parts by weight.

Examples of the polymerization terminating agent may be aromatic hydroxydithiocarboxylic acids such as hydroxyl amine, a hydroxyl amine sulfate,diethylhydroxy amine, a hydroxyl amine sulfonic acid and an alkali metalion thereof, a sodium dimethyl dithiocarbamate, a hydro quininederivative, a hydroxyl diethyl benzene dithiocarboxylic acid, and ahydroxyl dibutyl benzene dithiocarboxylic acid. The use amount of thepolymerization terminating agent is not particularly limited, but theamount is in a range of 0.1 to 2 parts by weight based on 100 parts byweight of the monomer.

Also, subsidiary materials, e.g., a pigment such as titanium oxide, afiller such as silica, a thickener, a chelating agent, a dispersant, apH adjuster, a deoxidizer, a particle size modifier, an antioxidant, oran oxygen scavenger, may be used if necessary during polymerization ofthe latex of the present invention.

In some cases, the polymerization reaction is stopped, and the latexresin of the present invention may then be obtained by removingunreacted monomers and adjusting a solid concentration or a pH value.

The present invention also relates to a composition for dip moldingcontaining the latex for dip molding.

In addition to the latex for dip molding, a vulcanizing agent and avulcanization accelerator may be mixed in the composition for dipmolding.

Examples of the vulcanizing agent typically used for dip molding may besulfurs, such as powdered sulfur, precipitated sulfur, colloidal sulfur,surface-treated sulfur and insoluble sulfur. The use amount of thevulcanizing agent may be in a range of 0.1 to 10 parts by weight basedon 100 parts by weight of the latex solid content and, for example, maybe in a range of 1 to 5 parts by weight.

Examples of the vulcanization accelerator typically used for dip moldingmay be 2-mercaptobenzothiazole (MBT),2,2-dithiobisbenzothiozole-2-sulfenamide (MBTS),N-cyclehexylbenzothiazole-2-sulfenamide (CBS),2-morpholinothiobenzothiazole (MBS), tetramethylthiuram monosulfide(TMTM), tetramethylthiuram disulfide (TMTD), zinc diethyldithiocarbamate(ZDEC), zinc dibutyldithiocarbamate (ZDBC), diphenylguanidine (DPG), ordi-o-tolyguanidine (DOTG). The vulcanization accelerator may be usedalone or in combination of two or more thereof. The use amount of thevulcanization accelerator may be in a range of 0.1 to 10 parts by weightbased on 100 parts by weight of the latex solid content and, forexample, may be in a range of 0.5 to 5 parts by weight.

The use amount of zinc oxide may be in a range of 0.1 to 5 parts byweight based on 100 parts by weight of the latex solid content and, forexample, may be in a range of 0.5 to 2 parts by weight.

Also, the composition for dip molding may include subsidiary materials,such as a pigment, a thickener, a chelating agent, a dispersant, a pHadjuster, a deoxidizer, a particle size modifier, an antioxidant, and anoxygen scavenger, if necessary.

The latex composition of the present invention may be prepared byperforming emulsion polymerization of a mixture of the each monomer, anda typical emulsion polymerization method may be used for the emulsionpolymerization.

A method of adding the monomer mixture is not particularly limited, andany method may be used among a method of introducing the monomer mixtureinto a polymerization reactor at a time, a method of continuouslyintroducing the monomer mixture into a polymerization reactor, a methodof introducing a portion of the monomer mixture into a polymerizationreactor and continuously introducing the remainder of the monomermixture into the polymerization reactor.

Polymerization temperature is not particularly limited, and thepolymerization temperature is usually in a range of 10° C. to 90° C. andmay be in a range of 25° C. to 75° C.

The present invention relates to a method of preparing a dip moldedproduct including: (a) dipping a dip mold in a coagulant solution toattach the coagulant onto a surface of the dip mold; (b) dipping the dipmold having the attached coagulant in the composition to form a dipmolded layer; (c) heat treating the dip molded layer formed on the dipmold to cross-link a latex resin.

Hereinafter, a method of preparing a dip molded product by using a latexcomposition of the present invention will be described in more detail.

(a) Dipping a dip Mold in a Coagulant Solution to Attach the Coagulantonto a Surface of the Dip Mold

Examples of the coagulant may be metal halides such as barium chloride,calcium chloride, magnesium chloride, zinc chloride, and aluminumchloride; nitrates such as barium nitrate, calcium nitrate, and zincnitrate; acetates such as barium acetate, calcium acetate, and zincacetate; sulfates such as calcium sulfate, magnesium sulfate, andaluminum sulfate. Calcium chloride and calcium nitrate may be used amongthe foregoing coagulants.

A coagulant solution is a solution in which the foregoing coagulant isdissolved in water, alcohol, or a mixture thereof. A concentration ofthe coagulant in the coagulant solution is usually in a range of 5 wt %to 75 wt %, and may be in a range of 15 wt % to 55 wt %.

(b) Dipping the Dip Mold Having the Attached Coagulant in theComposition to Form a Dip Molded Layer

The dip mold having the attached coagulant is dipped in a latexcomposition for dip molding prepared from the latex resin composition ofthe present invention, and a dip molded layer is then formed on the dipmold by taking the mold out of the latex composition.

A typical dipping method may be used for the foregoing dipping methodand, for example, a direct dipping method, an anode coagulation dippingmethod, and a Teague coagulation dipping method may be used. Among theforegoing methods, the anode coagulation dipping method may be usedbecause a dip molded product having a uniform thickness may easily beobtained thereby.

(c) Heat Treating the Dip Molded Layer Formed on the Dip Mold toCross-Link a Latex Resin

During heat treating, a water component is first evaporated and curingis then performed through cross-linking. Subsequently, the dip moldedlayer cross-linked by heat treating is removed from the dip mold toobtain a dip molded product.

Hereinafter, the present invention will be described in detail accordingto examples and comparative examples. The following examples are merelypresented to describe the present invention, and the scope of thepresent invention includes the scope defined by the following claims andmodifications or substitutions thereof and is not limited to the scopeof the present example.

EXAMPLE 1 1-1. Preparation of Latex for Dip Molding

A 10 L high-pressure reactor attached with an agitator, a thermometer, acooler, and an inlet of nitrogen gas and equipped so as to continuouslyintroduce a monomer, an emulsifier, and a polymerization reactioninitiator was filled with nitrogen, and 2 parts by weight of sodiumalkyl benzene sulfonate, 0.5 parts by weight of t-dodecyl mercaptan, 2parts by weight of sodium methallyl sulfonate, and 140 parts by weightof deionized water were introduced based on 100 parts by weight of amonomer mixture including 30 wt % of acrylonitrile, 66 wt % of1,3-butadiene, and 4 wt % of methacrylic acid, and heated at atemperature of 40° C.

0.3 parts by weight of potassium persulfate, a polymerization initiator,was introduced after heating and the polymerization was terminated byintroducing 0.1 parts by weight of sodium dimethyldithiocarbamate when aconversion rate reached 95%. Unreacted monomers were removed through adeodorization process and a carboxylated acrylonitrile-butadiene-basedcopolymer latex having a solid content of 45% and a pH of 8.5 wasobtained by adding ammonia water, an antioxidant, and an antifoamingagent.

Polymerization stabilities of the prepared latexes in parts per million(ppm) were calculated from an amount of impurities thereof based on asolid content after passing the latexes through 325 mesh and arepresented in the following Table 1. Amounts of scales in the reactor arepresented in the following Table 2.

1-2. Preparation of Composition for Dip Molding

A composition for dip molding having a solid content of 25% and a pH of10.0 was obtained by adding 1.5 parts by weight of sulfur, 1.5 parts byweight of zinc oxide, 0.5 parts by weight of zinc dibutyldithiocarbamate(ZDBC), a 3% potassium hydroxide solution, and an adequate amount ofsecondary distilled water to the latex. Stabilities of the preparedcompositions for dip molding in parts per million (ppm) were calculatedfrom an amount of impurities thereof based on a solid content afterpassing the latexes through 325 mesh and are presented in the followingTable 3.

1-3. Preparation of Dip Molded Product

A coagulant solution was prepared by mixing 22 parts by weight ofcalcium nitrate, 69.5 parts by weight of methanol, 8 parts by weight ofcalcium carbonate, and 0.5 parts by weight of a wetting agent (Teric320, produced by Huntsman Corporation, Australia). A ceramic mold havinga hand shape was dipped in the solution for 1 minute and removedtherefrom, and the mold having a hand shape was then coated with thecoagulant by drying at 70° C. for 3 minutes.

Next, the coagulant-coated mold was dipped in the composition for dipmolding for 1 minute and removed thereform, and the mold was thenimmersed in water or warm water for 3 minutes after being dried at 70°C. for 1 minute. The mold was again dried at 70° C. for 3 minutes, andwas then cross-linked at 125° C. for 20 minutes. A cross-linked dipmolded layer was peeled off from the mold having a hand shape to obtaina dip molded product having a glove shape.

EXAMPLE 2

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 1 except that 5 partsby weight of sodium methallyl sulfonate was used instead of using 2parts by weight thereof, and physical properties are presented in thefollowing Tables 1 to 3.

EXAMPLE 3

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 1 except that 10 partsby weight of sodium methallyl sulfonate was used instead of using 2parts by weight thereof, and physical properties are presented in thefollowing Tables 1 to 3.

EXAMPLE 4

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 1 except that 1 partby weight of sodium alkyl benzene sulfonate was used instead of using 2parts by weight thereof, and physical properties are presented in thefollowing Tables 1 to 3.

EXAMPLE 5

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 1 except that 35 wt %of acrylonitrile was used instead of using 30 wt % thereof and 61 wt %of 1,4-butadiene was used instead of using 66 wt % thereof, and physicalproperties are presented in the following Tables 1 to 3.

COMPARATIVE EXAMPLE 1

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 1 except that 2 partsby weight of sodium methallyl sulfonate was not used, and physicalproperties are presented in the following Tables 1 to 3.

COMPARATIVE EXAMPLE 2

A composition for dip molding and a dip molded product having a gloveshape were prepared in the same manner as Example 5 except that 2 partsby weight of sodium methallyl sulfonate was not used, and physicalproperties are presented in the following Tables 1 to 3.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 1 Example 2 Stability 31 25 91 61 24 1,279 986 [ppm]

TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 1 Example 2 Scale [g] 54 55 125 321 46 512 580

TABLE 3 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 1 Example 2 Stability 92 105 45 56 31 335 345 [ppm]

According to the results in Tables 1 to 3, excellent results wereobtained, in which the stabilities and scales of Examples 1 to 5 werelower than those of Comparative Examples.

EXPERIMENTAL EXAMPLE 1 Measurements of Physical Properties of Dip MoldedProduct

Test specimens having a dumbbell shape were prepared from the prepareddip molded product in accordance with ASTM D-412. Subsequently, the testspecimens were tensile tested at an elongation rate of 500 mm/minute byusing a universal testing machine (UTM). Tensile strengths andelongations at fracture were measured, and touches in terms of stress at300% elongation were measured. The results thereof are presented inTable 4. The higher the tensile strength and elongations were, thebetter the qualities of the dip molded products were. The lower thestresses at 300% elongation were, the better the touches and qualitiesof the dip molded products were.

TABLE 4 Tensile strength Stress at 300% (MPa) Elongation (%) elongation(MPa) Example 1 27.5 650 6.8 Example 2 26.5 640 6.9 Example 3 22.5 5808.7 Example 4 31.5 690 6.5 Example 5 33.1 610 10.1 Comparative 14.6 5206.2 Example 1 Comparative 17.8 460 9.6 Example 2

As shown in the results of Table 4, tensile strengths and elongations ofthe dip molded products prepared from the latexes of Examples 1 to 5according to the present invention were better than those of ComparativeExamples. In particular, it may be understood that the lower thestresses at 300% elongation were, the better the touches and qualitiesof the dip molded products were.

According to the present invention, a dip molded product havingexcellent tensile strength, elongation, and touch is provided, andlimitations, such as non-uniformity of physical properties anddifficulties in product management, may be resolved.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the present invention. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. A latex for dip molding comprising: a conjugateddiene monomer; an ethylenically unsaturated nitrile monomer; and anethylenically unsaturated acid monomer, wherein the latex furthercomprises a sodium methallyl sulfonate as a copolymerizable ionicmonomer, wherein the latex does not include a styrene monomer, andwherein the latex has a stability of about 24 ppm to 91 ppm.
 2. Thelatex for dip molding of claim 1, wherein the latex comprises about 0.1to 10 parts by weight of the sodium methallyl sulfonate based on 100parts by weight of a monomer mixture including about 40 to 90 wt % ofthe conjugated diene monomer, about 9 to 50 wt % of the ethylenicallyunsaturated nitrile monomer, and about 0.1 to 10 wt % of theethylenically unsaturated acid monomer.
 3. The latex for dip molding ofclaim 1, wherein the conjugated diene monomer is selected from the groupconsisting of 1,3-butadiene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 1,3-pentadiene, isoprene, and a mixture thereof.4. The latex for dip molding of claim 1, wherein the ethylenicallyunsaturated nitrile monomer is selected from the group consisting ofacrylonitrile, methacrylonitrile, fumalonitrile, α-chloronitrile,α-cyanoethyl acrylonitrile, and a mixture thereof.
 5. The latex for dipmolding of claim 1, wherein the ethylenically unsaturated acid monomeris selected from the group consisting of an ethylenically unsaturatedcarboxylic acid monomer, a polycarboxylic acid anhydride, anethylenically unsaturated sulfonic acid monomer, an ethylenicallyunsaturated polycarboxylic acid partial ester monomer, and a mixturethereof.
 6. The latex for dip molding of claim 1, wherein the latexfurther comprises about 0.1 to 20 wt % of other ethylenicallyunsaturated monomers copolymerizable with the ethylenically unsaturatednitrile monomer and the ethylenically unsaturated acid monomer amongtotal monomers.
 7. The latex for dip molding of claim 6, wherein theother ethylenically unsaturated monomers copolymerizable with theethylenically unsaturated nitrile monomer and the ethylenicallyunsaturated acid monomer are a vinyl aromatic monomer, afluoroalkylvinyl ether, an ethylenically unsaturated amid monomer, vinylpyridine, vinyl norbornene, a non-conjugated diene monomer, anethylenically unsaturated carboxylic acid ester monomer, and mixturesthereof.
 8. The latex for dip molding of claim 1, wherein the latex isemulsion polymerized by including one or more selected from the groupconsisting of an emulsifier, a polymerization initiator, a chaintransfer agent, a polymerization terminating agent, and a mixturethereof.
 9. The latex for dip molding of claim 8, wherein the emulsifieris selected from the group consisting of an alkyl benzene sulfonate, analcohol sulfate, an alcohol ether sulfonate, an alkyl phenol ethersulfonate, an alpha olefin sulfonate, a paraffin sulfonate, an estersulfosuccinate, a phosphate ester, an alkyl phenol ethoxylate, a fattyamine ethoxylate, a fatty acid ethoxylate, an alkanoamide, and a mixturethereof.
 10. A composition for dip molding comprising the latex for dipmolding according to claim 1.